1. Field of The Invention
The present invention relates to a glass plate bend-shaping apparatus and a method of bend-shaping a glass plate such as a window glass or the like for a vehicle. Particularly, the present invention relates to a bend-shaping apparatus provided with a positioning means for bend-shaping a front glass for a vehicle and a method of bend-shaping the front glass.
2. Discussion of Background
Generally, a glass plate used for, for instance, a window glass for a vehicle has been bend-shaped into a predetermined shape so as to meet the shape of a vehicle body or to obtain a streamline shape so that the resistance of air during cruising can be reduced. In bend-shaping the glass plate, a method of deadweight bending wherein a softened glass plate is mounted on a ring-like bending mold or a method using a vertical pressing furnace or a horizontal bending furnace has been conducted.
An example of the bend-shaping method using a horizontal bending furnace is disclosed in, for instance, U.S. Pat. No. 5,004,491. Namely, a glass plate heated in a heating furnace is transferred into a horizontal bending furnace by means of a transferring means comprising rollers. When the glass plate is moved to around the terminal point at a downstream portion in the horizontal bending furnace, the glass plate is held by a glass plate sucking and suspending device which is disposed at an upper portion of the furnace and the downstream side of the transferring means and which comprises an air suspension block (hereinbelow referred to as ASB) in which a number of orifices for ejecting air and a number of orifices for sucking air are formed in the entire area of the suspension surface of the device, by which the glass plate is held below the glass plate sucking and suspending device by a sucking force when air is sucked through the number of orifices.
The glass plate held below the glass plate sucking and suspending device is put on a lower mold for bend-shaping (hereinbelow, referred to as a lower mold) which is disposed below the glass plate sucking and suspending device. In this case, the glass plate is moved to the upper portion of the lower mold by means of the glass plate sucking and suspending device. Accordingly, there is no danger of the inclination or the deformation of the glass plate on the lower mold, and it can be correctly put on the lower mold. Then, the glass plate is pressed by lowering an upper mold for bend-shaping (hereinbelow, referred to as an upper mold) to the lower mold.
In order to fit the glass plate which has been bend-shaped to a vehicle body, the glass plate must be correctly bend-shaped so as to meet the shape of the vehicle body. In particular, when a laminated glass wherein an interlayer film such as a polyvinylbutyral film or the like is interposed between two glass plates for lamination is used for a front glass for a vehicle, it is necessary that the radius of curvature at any lamination part of the two glass plates corresponds, in its entirety or a partial portion, to each other when the laminated glass has been prepared. Otherwise, the glass plates may be broken in a pressing process in the manufacture of the laminated glass, may result in bubbles in the bonding plane in a long term use, or may result in peeling-off in the bonding plane. Accordingly, when the laminated glass having a curved surface is prepared, it is necessary to meet the radius of curvature in the laminated portion between the two glass plates. This requires the correct shaping of the laminated glass in comparison with the manufacture of a single plate glass window.
Since the shape and the radius of the curvature of the bend-shaped glass plate depend on the shape of a bend-shaping mold, the glass plate must be correctly put at a predetermined position on the lower mold so that a bend-shaping operation is precisely conducted. For this, it is necessary to put the glass plate on the bend-shaping mold after they have been correctly positioned and held by the sucking function of the glass plate sucking and suspending device. Specifically, a positioning means is provided below the ASB so that the positioning means is moved in parallel to the suspending surface of the ASB. The positioning means comprises metallic arm portions which are provided at both sides of the outside of the furnace and advanced into or retracted from the furnace, a glass plate supporting portion consisting of metallic circular plates provided at each of the top end of the arms. The glass plate is received by the glass plate supporting portions and is held at a predetermined position, and then, the glass plate is put on the lower mold.
In the above-mentioned bend-shaping apparatus, the glass plate is sucked by the glass plate sucking and suspending device so that it is suspended in a non-contact state at a position of about several mm, e.g. less than 1 mm away from the lower suspension surface of the glass plate sucking and suspending device. Accordingly, it was necessary to precisely control the distance between the glass plate sucking and suspending device and the arm portions of the positioning means so that the glass plate supporting portions can correctly support edges of the glass plate.
Since the positioning means of the conventional bend-shaping apparatus was so constructed as to advance to and retract from the furnace from the right and left sides of the furnace, the metallic arm portions were bent or deformed due to a temperature change in the advancing and retracting movements from the atmospheric temperature zone to the heating zone, or the repeating and stopping of a shaping cycle, whereby the distance between the glass plate and the glass plate sucking and suspending device differed from the distance between the glass plate supporting portions and the glass plate sucking and suspending device (FIG. 6). Accordingly, it was difficult to precisely put the glass plate on the bend-shaping mold.
When the bending of the arm portions resulted, it was necessary to adjust the height and the position of the arm portions in order to conduct precise positioning of the glass plate on the bend-shaping mold, this required the interruption of the bend-shaping processes, and much time and labor.